“On the first of the month [of Shevat], Moshe, inspired by prophecy from G-d, began to recite the words of the Book of Devarim to Israel.

…

[Thus] the first of Shevat is comparable to the day of the giving of the Torah… [and this day] remains forever suitable for the renewed acceptance of the Torah…

Because the period of transmission of the Book of Devarim was this thirty-seven day interval, all the days from the first of Shevat until the seventh of Adar are especially well suited for renewed inspiration in the study of Torah and the doing of Mitzvot.”